The present invention relates generally to packet communications systems and, more particularly, to a packet data communication system capable of providing control path/route redundancy capabilities in the process of performing remote control of access devices which are installed at user points.
In 1906, the leased-line telecommunication technology was first introduced in Japan in the form of a hotline which enables financial institutions to impart market conditions to each other on a real-time basis. Even today, after the elapse of more than one hundred years, the lease line is still expected to act as important infrastructure supporting mission-critical business services in national defense operations and financial and broadcasting activities, which are under requirements for higher security and reliability. Prior known lease line designs for physical one-to-one connection between users or subscribers are less in malfunction owing to simplicity of configuration. This ensures achievability of high security. In addition, it is easy to establish redundant paths for communications; so, it is possible to provide services of very high reliability. However, a user's exclusive possession of one line results in an increase in communication expense. This limits the usability so that a lease line is used only for supremely important communications of a special cooperate entity.
Meanwhile, packet exchange/switching networks using Ethernet™ lines have been explosively popularized, and components for use therein are becoming lower in cost and price owing to mass-production effects. In such packet switching networks, the use of virtual private network (VPN) technologies, such as virtual local area network (VLAN), multi-protocol label switching (MPLS) or like techniques, makes it possible to accommodate users in a logically completely separated network, thereby enabling securement of the security required. Furthermore, the standardization of new telecommunications architectures, including the operation administration and maintenance (OAM) for operation failure detection and the automatic protection switching (APS) for switching between communication paths, is being advanced—or has already been completed—in some entities, such as the International Telecommunication Union-Telecommunication Sector (ITU-T), the Institute of Electrical and Electronics Engineers (IEEE) or else. This contributes to appreciable improvements in fault tolerance. Accordingly, in recent years, lease line services using packet exchange networks become commercially available. This makes it possible to logically multiplex many users to one physical line, resulting in an abrupt decrease in communication charge for lease line services.
Unfortunately, this kind of lease line services using packet exchange networks are faced with the risk of large influenceability in communication cutoff events due to the fact that many users are logically multiplexed together to one physical line. One known countermeasure taken by most telecommunication carriers against this risk is to design communication paths by using the OAM and/or APS technique to have redundancy capabilities. However, it cannot be said that this approach is fully successful when supposing large-scale disasters occurring due to earthquakes, electrical power failures, etc. One traditional remedy for this problem is that a user makes contracts with a plurality of different communication carriers to thereby establish by himself the communication path redundancy. But, this does not come without accompanying penalties which follow: an increase in contract fee, and botheration as to the user's time-consuming and troublesome works including his or her manual operations for detecting an operation failure in a normally used communication network of one carrier and for switching it to a backup-side communication network of another carrier according to the user's own judgment on a case-by-case basis.
Recently, an advanced communication path redundancy service has become commercially available by business collaboration between different communication carriers. Providing this kind of service makes it unnecessary for users to manually switch between communication networks of such carriers. Instead, in order to establish the intended redundancy of the same level as traditional cases, users are required to install an extra dedicated device or equipment for achieving carrier accessability (referred to hereinafter as “user access device”) at every user base point and also to perform carrier switching at such user point. This user access device is needed to be managed by the carriers; however, a special-purpose network to be used by the carriers for device management—i.e., management network, such as network management system (NMS)—is unable to expand to the extent that covers these user sites. In view of this, attempts are usually made to perform the so-called “in-band” remote control using the same communication network as that for data transmission/reception.
It should be noted here that a carrier which is under direct contract with users is called the first carrier whereas a carrier which ties up with the first carrier to establish a backup communication pathway is called the second carrier. The user access device is the one that is designed for direct accommodation of users; so, this device is to be managed by the first carrier having direct contracts with these users. An exemplary system procedure therefor includes the steps of sending a control frame insertion command from a management network of the first carrier to a communication device of the first carrier, causing the communication device that received this command to generate a control frame, and sending this frame to a destination device—here, a target user access device that becomes the object to be controlled. This user access device notifies either its response or device alarm. To do this, it transmits the control frame to the communication device of the first carrier. This control frame is subjected to termination processing by the first carrier's communication device. Then, its contents are notified to the first carrier management network.
In the case of such in-band remote control, a control frame and usual data frames are sent together via the same communication path. Consequently, designing a usual frame transfer path to have redundancy leads to establishment of the redundancy of a remote control path. For example, in case the carrier's communication network is of the Ethernet™ type, Ethernet OAM or APS is employable in conformity to ITU-T Recommendation Y.1731 (OAM functions and mechanisms for Ethernet based networks), IEEE 802.1ag/D8.1 (Connectivity Fault Management), or ITU-T Recommendation G.8031/Y.1342 (Ethernet Protection Switching).